The present invention relates to hydrogenated styrene-modified dicyclopentadiene resins and their process of manufacture. More particularly, the present invention relates to thermally polymerized copolymers made from styrene and dicyclopentadiene monomers having relatively low odor, light color, and low molecular weights.
Various methods have been used to thermally copolymerize dicyclopentadiene (DCPD) feedstocks with vinyl aromatic hydrocarbons and hydrogenating these copolymer reaction products. Providing aromatic content to the resins influences compatibility with other polymers, and it is desired to achieve this compatibility property in combination with desirable softening point values, desirable molecular weights, low color, and other properties which are particularly useful in tackifier applications.
Numerous methods have been utilized to provide aromatic content to DCPD resins produced by thermal reaction processes. Typically a batch method is used where a vinyl aromatic material is charged along with DCPD to a thermal reactor and the combined mixture is heated to a reaction temperature typically in the range 240xc2x0 C. to 300xc2x0 C. to cause reaction and form a partially aromatic resin. An example is found in U.S. Pat. No. 5,171,793 where a mixture comprised predominantly of a crude vinyl aromatic feedstock ( C9 type feed containing principally methyl substituted styrenes and indene as reactive components ) combined with DCPD is charged batchwise to a reactor and heated to high temperature to oligomerize the reactants and form a resin product which was subsequently hydrogenated to produce a useful adhesive tackifier resin. This crude vinyl aromatic feedstock is a byproduct from petroleum processing.
An example of the use of a pure monomer aromatic feed in combination with DCPD is disclosed in U.S. Pat. Nos. 5,502,140 and 5,739,239 which disclose thermally polymerized copolymers of DCPD and xcex1-methylstyrene (AMS), which are subsequently hydrogenated. The use of higher levels of styrene was specifically acknowledged in these patent examples to produce resin products with undesirable high molecular weight characteristics, and the preferred use of AMS over styrene for producing thermal DCPD copolymer resins was specifically identified in these patent examples.
In the DCPD thermal reactions such as those described in U.S. Pat. Nos. 5,171,793, 5,502,140 and 5,739,239 only a fraction of the reactive vinyl components in the batch charge (hereafter referred to as reactives) are converted to resin during the thermal reaction. Typically between 50% to 75% of the reactives in the batch charge are converted to resin product during the thermal reaction. The residual reactives possess sufficient chemical reactivity that they could be further converted to resin by physically separating them from the resin product (e.g. by vacuum stripping ) before hydrogenation and recycling these recovered reactives into a subsequent batch charge. Due to the relatively low reactivity of AMS, relative to vinyl aromatics such as styrene, in U.S. Pat. Nos. 5,502,140 and 5,739,239 only about 50% of the AIMS in the starting charge is consumed during the thermal reaction, requiring the remainder to be recycled back into the process. The presence of high levels of AMS in combination with unreacted olefin materials derived from DCPD in the recycle from a thermal reaction makes it difficult to accurately characterize the recycle composition and subsequently determine the composition of the batch charge (containing recycle) which is used in a subsequent thermal reaction. This makes it difficult to produce a consistent thermal resin product when recycle is used.
Additionally, while these resins produced from DCPD and AMS have been found to be useful, their colors are often darker than desired, even after hydrogenation. Hydrogenation of thermal DCPD resins is utilized to eliminate olefin unsaturation, reduce or eliminate color, and to controllably reduce the aromatic nature of the resin in order to obtain desired properties. Depending on the catalyst chosen, hydrogenation can selectively remove color rather than eliminate aromatic content, so that lighter colors can be obtained through hydrogenation without significantly reducing the aromatic content of the resin. It is desirable to produce a thermal polymerization product that does not require extensive hydrogenation of aromatic functionality which increases the required hydrogen consumption and causes other process difficulties. Additionally it is desirable that thermal DCPD resins can be hydrogenated to light colored products without excessive hydrogenation time or excessively severe hydrogenation conditions. Generally, it is desirable to produce an aromatic modified DCPD thermal resin which has the required aromatic content for compatibility requirements and which can be hydrogenated to a light colored resin without significantly hydrogenating the aromatic content of the resin.
Using styrene instead of AMS in thermal reactions in combination with DCPD was found to produce lighter colored resin products, with low aromatic content, making it easier to hydrogenate the products to light colored tackifier resins. Additionally styrene, and similar vinyl aromatic monomers, are more active than AMS in thermal reactions and a higher conversion of styrene, or similar vinyl aromatic, to resin product is achieved as compared to AMS.
Using styrene to produce resin products with the desired aromatic content and tackifier properties, it would be desirable to incorporate from about 10% to about 25% styrene into the resin. However as learned from U.S. Pat. Nos. 5,502,140 and 5,739,239 this level of styrene produces resin product with an undesirable high molecular weight which is a disadvantage when the resin is used as an adhesive tackifier. This high molecular weight characteristic may be due to the formation of high molecular weight polystyrene by thermal initiation at the high temperatures required to form resins from DCPD.
U.S. Pat. No. 2,689,232 to Gerhart in 1954 teaches a method of copolymerizing CPD and vinylic hydrocarbons in a batch process. In order to avoid homopolymerization, the comonomers are cold-added to an autoclave and thereafter heated and pressurized for a holding period of two to six hours to accomplish the reaction. The extent of the reaction is controlled by timing the removal or reduction of heat. The resultant resin from this process is either brittle, or dark, or possessed of other undesirable properties for tackifier applications. As such, the patent teaches the use of an oil to dissolve the resin for useful applications.
EPO 0845484 A2 discloses the reaction of stoichiometric amounts of styrene and DCPD, with subsequent adjustment of aromatic content through hydrogenation. Disclosed reaction times range from 3.5 to 10 hours. In this example a high level of styrene was incorporated into the resin and extensive hydrogenation of the aromatic content was required to achieve the desired final resin color and compatibility properties.
It would be desirable to utilize styrene under reaction conditions that provide thermally polymerized resins based on DCPD monomers which have desirable aromatic content of about 10% to about 25% styrene, relatively low molecular weights, relatively high softening points, which do not contain significant amounts of polystyrene in the final resin product.
It would also be desirable to provide thermally polymerized resins and a process for producing such resins which achieve the desired aromatic content without the need for subsequent process adjustments.
It is further desirable to provide a method of production that offers near complete conversion of reactants to resin product in relatively short reaction times.
It would also be desirable to be able to run the thermal reactions to reduce or eliminate the formation of crystalline the DCPD wax which leads to plugging of filters during typical processing of DCPD resin products.
Lastly it is desirable to provide a method for producing DCPD thermal resins with aromatic content that requires less severe hydrogenation conditions for producing a light colored tackifier resin.
The present invention includes a method of thermally producing styrene-modified DCPD resins which have a desirable aromatic content, relatively low molecular Weight, low color and relatively high softening points. In one aspect of the invention, there is included a resin which is the reaction product comprised of (1) about 5% to about 25% by weight of a compound of the formula: 
wherein R1 is H, C1-10 linear or branched aliphatic or aromatic, OH or OR, and R is alkyl or acyl; and (2) about 95% to about 75% by weight based on the total monomer content of a cyclic diolefin component comprising at least about 50% by weight dicyclopentadiene, said product containing minimal levels of high molecular weight styrenic polymer and exhibiting desirable low molecular weight characteristics. The resultant resins are desirably hydrogenated at least partially to form thermally stable derivatives.
In another aspect of the invention there is included a method of producing an aromatic-modified resin having a Mz of less than 2000 comprising the steps of: (i) providing solvent or a mixture of solvent and recycled reactives to a reactor, said recycled reactives comprised of DCPD and olefins and reactive oligomers derived from DCPD, along with low levels of styrene monomer (ii) heating said solvent or recycled reactants to a temperature of about 200xc2x0 to about 260xc2x0 C.; and (iii) adding a mixture comprised of about 5% to about 25% by weight styrene in combination with about 95% to about 75% DCPD monomer, into the reactor at the referred to temperature, at a rate to consume styrene monomer at the rate at which it is added such that the concentration of free styrene monomers in the reaction medium is held at a minimum at any given time of the reaction, e.g. less than about 5% by weight of the total reaction mixture.
In a variation of this invention a portion of the DCPD added to the reactor in combination with styrene at elevated temperature (step iii) can be instead added during the initial batch charge (step i) while maintaining the same ratio of fresh DCPD and styrene monomer added to the reaction. This requires that the level of styrene in the styrene/DCPD mixture added at the elevated temperature (step iii) be appropriately increased.